Suspension for crane booms



June 1945- T. o. DAVIDSON 2,378,915

SUSPENSION FR CRANE BOOMS Filed NOV. 13, 1943 Patented June 26, 1945 SUSPENSION FOR CRANE BOOMS Trevor 0. Davidson, Milwaukee, Wis... asslgnor to Bucyrus-Erie Company, South Milwaukee, Wis., a corporation of Delaware o Application November 13, 1943, Serial No. 510,098

' 3 Claims. (Cl. 212-144) My invention relates to new and useful-im provementsin suspensions for crane booms, more particularly for the very long booms on that type of crane known as dragline excavators.

It has been found that, in the case of a long slender inclined boom, suspended by guysextending from an A-frame on the base of the machine to the outer point of the boom, there is a distinct sag in the middle of the boom, when the boom is not under load. When a loadis added to the hoist rope whichpasses from a winch on the base of the machine, thence over a sheave at the point of the boom, the end-toend compression in the boom, due to the resultant of the tension in the hoist rope and the suspension guys, greatly and dangerously increases this downward bend at the middle'of the boom.

To obviate this sag and bend, the conventional expedient has been to run a second set of guys from the A-frame to the middle of the boom. This eliminates the above discussed initial sa and consequent bend,'but only so long as the two sets of guys remain in perfect and exact relative adjustment. If the center guys become disproportionately stretched, they do not prevent the discussed tendencies. Whereas, if the long guys become disproportionately stretched, the center guys will impose an initial upward bend in the boom, which will become greatly and dangerously increased with the addition of a load on the hoist rope; and there will be nothing t0,resist this bend.

invention to devise a boom suspension, effective automatically to prevent excessive and danger- Accordingly, it is the principal object of my main frame of a crane. Pivoted to the front thereof, and extending forwardly diagonally upward, is a boom l2. Also pivoted to the front of the main frame II, and extending forwardly diagonally upward at a steeper inclination, is a strut I3, This strut is supported by boom-hoist ropes II from the top of A-frame l5.

Thestrut l3 need not be separately pivoted to the main frame. As shown, its foot is integral with the foot of the boom, inasmuch as the flexibility of these two elements is sufilcient to produce the same efiect-(within the scope of their very limited relative movement) as though they were separately pivoted to the main frame.

Fixed-length guys l6 extend from the top of the strut to the outer end of the boom l2. Short the point of attachment of the, short suspension members I! thereto.

The length of these suspension members is so selected that, under the influence of the normal maximum expected load, the increased tension in the guys will flatten the angle in the guys sufficiently to straighten out the sag in the boom exactly, or practically so.

One by-product ormy invention is, of course, to reduce the whip in the boom under live loads, but this advantage is also attained by the priorart device discussed earlierherein.

My invention consists in the novel parts and i in the combination and arrangement thereof,

which are defined in the appended claims, and of which one embodiment is exemplified in the accompanying drawing, which is hereinafter particularly described and explained.

Throughout the description the same reference number is appliedto the same member or to similar members.

we see that l l is the The guys need not be ropes; other sorts of tension members, capable of angular, or even non-angular, bending at the point of attachment oi the suspension members, would suflice, al-

though ropes are simpler, being easier to rig and adjust. And similarly the suspension members themselves need not be still, since they carry merely tension.

TheA-frame need not be in A-fraine form;

hence the use of the word "A-frame in the claims intends an A-irame or equivalent.

The importance of having the guys l6 be fixedlength should be stressed. For if these guys were a merely reaches of the boom-hoist ropes II, it would be nearly impossible to maintain a proper adjustment of relative lengths.

during operations; but also maintains this component during raising and lowering the boom, whereas this component would nearly vanish in 'iully lowered position, if the strut wereomitted.

, ore, the presence oi. the strut facilitates a permanent adjustment or the proper rel ative lengths of guys It and suspension membersll.

The hoist rope l8 runs from a when I 9 on the main frame ll, over a sheave 20 on the strut l3,

thence over a sheave II at th outer end or the boom, and thence downwardly to the load (not shown) to be lifted thereby. Otheriairlead means thansheave 20 could be employed, or such meafis could be omitted. 4 I

Having now described and illustrated one form of my invention, I wish it to be understood that my invention is not to be limited tothe specific form or arrangement of parts herein described and shown, except as specifically limited by my claims. Iclaim:

1. In a suspension for a long slender upwardly inclined crane. boom, the combination of an A- frame adjacent the foot of the boom; an upwardly from the middle of the uys to the middie or the boom, so as to permit .an initial sag in wardly' projecting strut, between the A-fraine and the boom, and pivotally mounted adjacent the foot of the boom; fixed-length guys from the upper end (if the strut. to the outer end of th boom; means for supporting the strut from the A-irame; and fixed-length suspension means for the boom, extending downwardly from the middle of the guys tothe middle of the boom, so as to permit '3 v e gamers I I aninitial sagin the boom, but so as tostraightenthe boom, when the guys straighten under influence of a load on the outer end of the boom; the length of said suspension means being slightly less than the distance, from its point of attachment to the boom, to a straight line drawn between the two ends of the guys, when the boom is not under load.

'2. In a suspension for a long slender upwardly inclined crane boom, the combination of an upwardly projecting member adjacent the foot of the boom; fixed-length guys from the upper end or the upwardly projecting member to the outer end 01 the boom; means for supporting the upwardly projecting member and fixed-length suspension'means for the boom, extending downthe boom, but so as to straighten the boom, when the guys straighten under influence or a load .on

the outer end of the boom; the length of said sus- 

